In many wells, it may be difficult to run the casing to great depths because friction between the wellbore and the casing often results in a substantial amount of drag. This is particularly true in horizontal and/or deviated wells. In some cases, the drag on the casing can exceed the available weight in the vertical section of the wellbore. If there is insufficient weight in the vertical portion of the wellbore, it may be difficult or impossible to overcome drag in the wellbore.
Various attempts have been made to overcome this drag and achieve greater well depths and/or to achieve a horizontal well. For example, techniques to alter wellbore geometry are available, but these techniques can be time-consuming and expensive. Techniques to lighten or “float” the casing have been used to extend the depth of well. For example, there exists techniques in which the ends of a casing string portion are plugged, the plugged portion is filled with a low density, miscible fluid to provide a buoyant force. After the plugged portion is placed in the wellbore, the plugs must be drilled out, and the low density miscible fluid is forced out into the wellbore. The extra step of drilling out increases completion time. Some flotation devices require a packer to seal the casing above the air chamber. In these cases, the chamber is sealed at its upper end by a packer. The packer may be removed from the casing string using a conventional drill-type workstring, for example.
In many casing float techniques and devices, it may not be possible to achieve full casing ID (inside diameter) following the opening of the air chamber. It is desirable to achieve full casing ID so that downhole tools can be conveyed to this region of the casing string and so that operations, such as cementing can be easily carried out using conventional ball-drop techniques, or other conventional techniques. Also, many float devices require the use of specialized float shoes and/or float collars.
It would be desirable to have a flotation chamber (also referred to herein as a “float chamber” or “buoyant chamber”) which is easy and relatively inexpensive to install on a casing string and which can be used with conventional float equipment such as float shoes and float collars, and with conventional equipment such as landing collars and cementing plugs. Further, it would be desirable if the parts of the float chamber could be easily removed from the wellbore and/or that the removal could result in full casing ID so that various downhole operations could be readily performed following removal or opening of the buoyant chamber.